[PATCH] gpio: pca953x: fix pca953x_irq_bus_sync_unlock race

[Ian Ray <ian.ray@xxxxxxxxxxxxxxxx>]

Ensure that `i2c_lock' is held when setting interrupt latch and mask in
pca953x_irq_bus_sync_unlock() in order to avoid races.

The other (non-probe) call site pca953x_gpio_set_multiple() ensures the
lock is held before calling pca953x_write_regs().

The problem occurred when a request raced against irq_bus_sync_unlock()
approximately once per thousand reboots on an i.MX8MP based system.

 * Normal case

   0-0022: write register AI|3a {03,02,00,00,01} Input latch P0
   0-0022: write register AI|49 {fc,fd,ff,ff,fe} Interrupt mask P0
   0-0022: write register AI|08 {ff,00,00,00,00} Output P3
   0-0022: write register AI|12 {fc,00,00,00,00} Config P3

 * Race case

   0-0022: write register AI|08 {ff,00,00,00,00} Output P3
   0-0022: write register AI|08 {03,02,00,00,01} *** Wrong register ***
   0-0022: write register AI|12 {fc,00,00,00,00} Config P3
   0-0022: write register AI|49 {fc,fd,ff,ff,fe} Interrupt mask P0

Signed-off-by: Ian Ray <ian.ray@xxxxxxxxxxxxxxxx>
---
 drivers/gpio/gpio-pca953x.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
index 77a2812f2974..732a6964748c 100644
--- a/drivers/gpio/gpio-pca953x.c
+++ b/drivers/gpio/gpio-pca953x.c
@@ -758,6 +758,8 @@ static void pca953x_irq_bus_sync_unlock(struct irq_data *d)
 	int level;
 
 	if (chip->driver_data & PCA_PCAL) {
+		guard(mutex)(&chip->i2c_lock);
+
 		/* Enable latch on interrupt-enabled inputs */
 		pca953x_write_regs(chip, PCAL953X_IN_LATCH, chip->irq_mask);
 
-- 
2.39.2